Oxygen substitution and sulfur vacancies in NaBiS₂: a Pb-free candidate for solution processable solar cells

High performance bismuth-based semiconductors are attractive large atom containing candidates needing further development. Theoretical investigations of defect mechanisms in NaBiS2 have been performed using PBE GGA functionals. Effective masses are estimated at the band extrema and found to be 0.36m0or less. High levels of oxygen substitution and significant sulfur deficiency lead to a loss of the fundamental bandgap. Lattice parameters for the defective materials have been derived and provide an experimental signature for high levels of these defects. The work informs the development of promising but little explored lower symmetry bismuth compounds for solar energy applications.